C win (3/3): postpone init2 after dl_init, GvCV_set of XS init init2

apply 3/3 win patch, fixes perlcc --staticxs
C 5.18: fix dynamic COW strings

add COW \0\1 REFCNT to dynamic strings.
fix wrong CUR for PVMG magic strings by passing the already calc. cur from
save_pv_or_rv to savepvn.

This fixes many 5.19.6d-nt-asan bugs.
Still failing C,-O3:
  method_named: 12,15,35,42-45,50,72,74,75,81,90,152,159,176,179,183,195,196,
  reg_temp_copy: 33,143
  pad_push: 99,165
  ckwarn_common: 156,174,175,184,192,207,232,243
  sv_resetpvn: 188
  do_eval: 250